Last week, the Lincoln Near-Earth Asteroid Research (LINEAR) sky survey program, designed to sweep the heavens looking for near-Earth asteroids, spotted something really weird; an elongated streak that looked as if two asteroids had collided. Just days later, Hubble was pointed at the object, and what it saw was really really weird:

[Click to armageddonate.]

This is a false-color image showing the object, called P/2010 A2, in visible light. The long tail of debris is obvious; this is probably dust being blown back by the solar wind, similar to the way a comet’s tail is blown back. What apparently has happened is that two small, previously-undiscovered asteroids collided, impacting with a speed of at least 5 km/sec (and possibly faster). The energy in such a collision is like setting off a nuclear bomb, or actually many nuclear bombs! The asteroids shattered, and much of the debris expanded outward as pulverized dust.

Now, let me just take a moment and say HOLY HALEAKALA WHAT WE’RE SEEING HERE IS THE COLLISION BETWEEN TWO PREVIOUSLY UNDISCOVERED ASTEROIDS THAT EXPLODED LIKE THERMONUCLEAR WEAPONS WHEN THEY IMPACTED!!!

Phew. OK, I feel better. I needed to get that off my chest.

First off, to be clear we’re in no danger from this event. It was really far away (in human terms; 140 million km or 90 million miles — the object’s orbit keeps it farther from the Sun than Mars — so we’re not about to get pummeled with debris. And while the explosion energy was quite large — certainly much larger than any weapon ever detonated on Earth — it wasn’t radioactive, in case you’re worried about that sort of thing. This was a kinetic explosion, caused by a high-speed collision, and not an actual detonation of any kind.

Looking at the image, the bright spot to the left is most likely what’s left of one of the two asteroids, a chunk of rock estimated to be a mere 140 meters (450 feet) across. In the press release they’re not clear about the curved line emanating to the right of the nucleus. It may be — and I’m spitballing here — dust blown back from a stream of chunks, since the tail is broad and appears to originate from that swept curve, and not from the nucleus itself. The other filament perpendicular to the curve is from yet another piece of debris.

Despite how much this looks like a comet, ground-based observations indicate no gas is present, meaning this was from asteroids colliding, not comets, which have significant amounts of ice which turn to gas near the Sun. The collision energy was high enough to produce a lot of gas if any were present. That clinches this being an asteroid impact.

Also, the orbit of the object indicates it’s an asteroid, and it appears to be part of a well-known group of asteroids called the Flora family, which share similar orbital characteristics, and are probably remnants themselves of an ancient breakup of a much larger parent asteroid.

Nothing like this has ever been seen before. Sure, Hubble and about a hundred other telescopes observed the comet Shoemaker-Levy 9 slam in to Jupiter in 1994, but that was different than seeing two asteroids hit. Asteroids are small, and very very far apart on average (don’t believe scenes like that in "Empire Strikes Back"), so a collision like this is extremely rare, and catching it from such a great vantage point rarer still. But we have a lot of eyes on the sky, and the more we watch the more we’ll see.

And we’d better. An object 140 meters across hitting the Earth would, to be technical, suck. Hard. Whatever caused Meteor Crater in Arizona, an impact scar over a kilometer across, was itself probably about 40 meters across. An object like 2010 A2, which is three times the diameter, would have 20 -30 times the mass, and do considerably more damage. I’m glad groups like LINEAR are out there patrolling the skies for such things. We need to learn as much as we can about these asteroids, so that we can prevent the next Meteor Crater from occurring.

But a question : Who gets to name the rock(s) that are left? Does each particle and fragment spotted get its own minor planet number or does the whole mess get given a collective name of the discoverers choice? (Eg. asteroid Vesta, Ceres, Plait, Asimov etc ..)

Plus I guess it finally (almost) justifies the old and common typo of “cemetry dust” instead of cometary dust in space! 😉

PS. Yes, I know we’re talking asteroid here not comet even if it does look awfully comet-like. Any idea what the magnitude of the object was like & how bright it might’ve looked at impact seen from Earth?

Also, I think it’s interesting that two asteroids in the same group (the Flora family) can have such a large differential speed (5 km/sec).

I would have thought they were also coasting along at the same relative speed just like a family on a driving vacation. “look kids, there’s Mars. And hey, there’s the Trojan asteroid family. Say hello!”

That is pretty cool! Although I keep thinking about the HUGE leap between detecting and knowing about objects in the sky that could make things “suck hard” down here, and actually DOING somethig about them.

“One question. If they share orbital characteristics how did they hit each other with such a difference in velocity?”

Their orbits are similar in that they fall within a broad but defined spectrum of orbital configurations. Even within that spectrum any two colliding objects will still have considerable relative velocity.

It’s like when a spacecraft launched from Earth rendezvous with an already orbiting satellite, such as the ISS. The spacecraft must trim its orbit as it approaches the target so that there’s as little relative velocity as possible just as they meet. Otherwise it’s just a collision. Without all the fine-tuning it’s improbable that two asteroids will meet at zero relative velocity. From the spectrum of orbits of asteroids, it’s possible to put a lower limit on how fast to expect them to be moving with respect to each other just as they smack.

The LSST group estimates that there is a catastrophic disruption of one 10m class object every day in the main belt, and they expect to image approximately one of these explosions every week!

If anyone is curious about the family these guys came from, here’s a plot of the largest asteroid families in orbital-element space, with colors representing the SDSS photometric colors of each asteroid:

@JKessler: Darnit! I came into the comments to post that very thing. It is obviously a Bird of Prey coming out of warp in an astroid field. I’m sure the captain disintegrated the navigator for flying them into an astroid before the ship came completely apart.

however…the title of this blog is “bad” astronomy and this post is clearly “good” astronomy. when you gonna start posting about “bad” astronomy and other stuff that is not even tangentially related to “bad” astronomy!!! geez!!!

heres a question, now that I think of it: What’s the movement of the object relative to the debris tail? I know the orbit is not precise yet, but is there a rough idea? is it perpendicular to the tail, parallel, or what?

“heres a question, now that I think of it: What’s the movement of the object relative to the debris tail? I know the orbit is not precise yet, but is there a rough idea? is it perpendicular to the tail, parallel, or what?”

Good questions. If the debris were mostly just dispersing more or less tangentially to the overall orbital path, it should be more homogenous. Instead the distribution has that sharp edge with debris tapering off gradually in one direction. Smaller asteroids tend to be aggregates of gravel held together mainly by gravity, so the collision probably generated a lot of small, fine particles. The smaller the particle the less surface area it has relative to its mass, so the solar wind pressure plays a bigger role in those particles’ futures than it did when they were all stuck together. So the solar wind is blowing the fine debris radially away. Since the orbits of that family of asteroids have low eccentricities, the radial motion of the debris is close to perpendicular to the overall orbit.

This is better then the fx in a scifi movie or even in the video game asteriods(or the hard as heck sequal asteriods deleux) by the way is any debrie heading for Earth like in the movie meteor?and do we need to worry about it?

I thought it was ET sacrificing themselves to save the Earth from that dastardly asteroid, just like Tunguska in 1908.

Seriously, I wonder what the composition of the debris cloud is, and how it compares to debris disks seen around other stars, especially sun-like stars? How long will astronomers be able to track this asteroidal dissection and will they be able to detect signs of space weathering of the debris? Will a pronounced debris stream now form, similar to those observed relating to meteor showers (i.e. similar to Phaethon)….even though we’ll miss out on a new shower? Lots of questions!

Can we track back the debris motion to determine probably impact date/time?

If there is no discernible motion in the debris stream, is it possible that the collision occurred a long time ago? Or at all? i.e. could it be a result of centripetal force destruction. Perhaps the asteroid had a minor impact that set it spinning, then it broke up, spraying debris that also inherited the majority of the objects orbital velocity.

Uselesstwit @ #5 asked: “If they share orbital characteristics how did they hit each other with such a difference in velocity?”

Where does it say they shared orbital characteristics? I couldn’t find any reference to it.

My thought, for what it’s worth, is that the object which didn’t survive the collision could easily have been on a very different orbit. For example, it could have been on a more elongated orbit, meaning the collision was more like a sideswipe than a head-on (like a bad merge onto a freeway).

I’m glad that LINEAR is out there patrolling the skies too. Too bad that they are only good for seeing things after they hit something. If anybody thinks that We (earthlings) will avoid any and all NEA collisions just because someone is keeping an eye peeled, is fantasizing, as in science/fantasy. Some day there will be another new meteor crator, and that will be the end of this story. Even if We (earthlings) develop new devices such as ground or space borne laser cannons, etc. we will not be able to stop this inevitable meeting.

WHAT WE’RE SEEING HERE IS THE COLLISION BETWEEN TWO PREVIOUSLY UNDISCOVERED ASTEROIDS THAT EXPLODED LIKE THERMONUCLEAR WEAPONS WHEN THEY IMPACTED!!!

I seem to have picked up a slight case of picayunitis, but…

The asteroids did not explode “like thermonuclear weapons.” There was no fission or fusion; just a whopping great bang resulting from a pretty fair amount of kinetic energy released in a very short amount of time.

Thank you for channeling the thoughts of all others, T.E.L. [edit: bah! you cut it out before my snappy reply could be posted!]

My picayuniness was based on a common theme of the good doctor BA’s. T’wit: science is about reality. Reality is cool in and of itself.

Similes are neat-o, but any time a “nuclear” comparison is made, one runs the risk of some negative fallout (snicker), in this case a gullible public and/or media that might see the good doctor BA’s comment and conclude that, OH MY GOD! SPACE IS FILLED WITH RADIOACTIVE ASTEROID DUST BECAUSE THEY BLEW UP LIKE ATOM BOMBS AND DEAR LORD SAVE US FROM THIS HORRIBLE MENACE FROM SPACE!

Nice piece! The fragment also kind of resembles a Klingon Bird of Prey. So exiting! Anyway, from the post’s reference to Star Wars asteroid belt I stumbled onto the “The Science & The Fiction” gallery and there the entry for Deep Impact. In the “Bad” part you write that blowing up a comet into “millions of pieces of ice and rock” would not be enough, as those pieces would still “lay waste to our planet”. I’d like a little further explanation of this if possible (a link will suffice if it’s been explained before).

What I mean is that there is a roughly known size constraint of how large a meteor has to be for it to make it through the atmosphere and hit ground. Now if the miles wide asteroid was blown to pieces that are all smaller than this, what would that mean for it’s damage potential? Individually none of those pieces would make an impact on ground but would burn “harmlessly” in the atmosphere. Certainly that makes for less danger than a big ground impact?

Is the case different when there are not a few dozen but a few million of such pieces coming at us simultaneously or does the movie plot imply the pieces are still big enough to reach surface?

The time-lapse footage of this will be the kicker; over the next few weeks & months more images need to be made to follow the progress of the fragments. Will smaller scopes be able to share in the fun?

“Now, let me just take a moment and say HOLY HALEAKALA WHAT WE’RE SEEING HERE IS THE COLLISION BETWEEN TWO PREVIOUSLY UNDISCOVERED ASTEROIDS THAT EXPLODED LIKE THERMONUCLEAR WEAPONS WHEN THEY IMPACTED!!!”

The energy was, the temperatures, products output, and brisance were NOT like thermonuclear weapons (actually called nuclear bombs or nuclear explosives because the fusion mechanism is not thermally driven but rather pressure driven, indeed high temperatures are the enemy of nuclear bombs because they scatter the fusion fuel and prevent complete compression.)

Not exactly the best post for this, but I stumbled across it and knew you’d love it- it’s a walkthrough of the scale of the universe. Feel free to delete/relocate this post, but just check out the link- it’s a walkthrough of the scale of the universe and deserving of a post of it’s own; it totally describes the awe of the scale of the universe.

morgajel, I posted about this a few days ago. In fact, I didn’t see any hint of it on the web before I put it here, and a few days later I saw links to it in other blogs as well. So I suspect we’ve come full circle here.

Love the blog.
1. To solid odjects coming together and spitting into many pieces with heat generated (possibly)… IS fission. Macro Fission (not nuclear fission) in this case.
2. If these two astroids are conglomerates there might not have been much of a flash.
3. Rate of expansion of the dust tail versus the speed/force of the solarwind would give you a good aproximation of where the collision occured relative to earth. But that location is a moot pointas the explsion is right in front of us (so to say) as the X or its center marks the spot.
4. That said if we know the location in space of the collision some telescope might have been pointing at it at the moment or shortly after.

Anyway… not wanting (so why am I mentioning this?) apocalypise this photo, but Throne of Fire comes to mind. (see that great bible passage Mark chap 23 for one of the best meteor impact warnings and advice passages in ancient texts)

Holy Haleakala! For the second time this day I’m struck with awe!
First there was the astronomy picture of the day (from Haleakala, with the brilliant Mars and moon-induced fogbow combination!), then there was this.

What a ridiculously rare chance that must’ve been. Its chance is maybe even worse than that of two very tiny insects flying at random in a sporting dome. I mean, 1 mm would’ve been enough for a miss, and this must’ve been a fairly nice direct hit.
Very cool indeed! (as long as they stay away from our planet, good thing some of them smash up like this)

Any chance Cassini, MRO, Mars Express or New Horizons could image this? Any of the comet/asteroid missions?

I don’t know for sure but I strongly suspect they’d all be too far away to do so.

Cassini is orbiting Saturn & to spy anything in the asteroid belt it’d have to look near our Sun. Remember that for Saturn the planets inside its orbit (Jupiter, Mars, Earth, etc ..) will be clustering close to the Sun & never moving far away from its glare – just like Venus and Mercury are “Evening & Morning stars” only visible in or near dusk & dawn as seen from our earthly skies.

Same thing applies to NewHorizons & I’m not sure if that even has its cameras on or if they’re turned off until it gets much nearer to Pluto. (Yes, it photographed Jupiter but I think they may have turned the cameras off for a while afterwards during the years-long “cruise” to save power. Not sure whether that’s the case but think that’s plausible.)

From Martian orbit where the Mars Reconnaissence Orbiter & Mars Express are there’s the advantage of being inside the asteroid belt’s orbit so this asteroidal mess won’t be lost in the Solar glare and their also closer and their cameras are definitely working well. But still those cameras are not really designed for telescopic observations of faint & distant objects in space but rather for surveying the martian terrain close below them.

The asteroid belt is very big and this object is unlikely to be that bright so even if the MRO or Mars Express or other spaceprobe mission did manage to spot this object its very unlikely they’d get any images better than telescopes here or in Earth orbit.

I think I saw this all take place in the sky last night. I saw it around 9:15 MST in Idaho in the Eastern Sky! It was pretty large…looked as if a plane was on fire and falling to the ground. AMAZING!!!!

Wait – how can you say “Hubble captures picture of asteroid collision!”, when according to that well-know scientific journal, The Sun newspaper, you space-boffins are supposed to be utterly baffled by this “space UFO”?

This does not look like two asteroids happend to have a collision.Some one is lying.Scientist should stop peddling this trick.What it does look like though is some sort of space craft and is quiet a mystery.This mourning I saw a news commentater and a scientist talking about this on fox tv, and they sounded non smart. This is some sort of craft or a fake?,but the collision of two asteroids is highly doubtful.Some times scientist like to peddle stupid theory’s. please comment on this comment.
Thanks
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If you think it’s a spacecraft, not the leftovers from an asteroid collision, then here’s your chance: Explain your reasoning. Explain what you think is spacecraft-like about it. Explain what’s so non-asteroid-collision-ish about it. Present your case, in detail.

I find some of this highly unlikely, considering the X debris cloud is what, maybe a couple miles wide? At the energy levels expected, it would be couple miles wide less than a few seconds after the impact, which would require some other theory for the long plume.

I don’t believe the long plume trail and the X mark are related to each other. The long plume trail couldn’t be generated via solar wind in any short period of time that would come about from a high energy impact.

They will need to take multiple photos over time to get an idea of the speed of the white object and the debris expansion. Anything without that is complete speculation and a finding of an asteroid collision is, at best, a guess.